The present invention relates generally to stepper motors and more particularly to a circuit for initiating deceleration of a stepper motor.
It is well known in the art of stepper motors that there are basically two modes of operation. The first mode is low speed operation, often designated "error free start stop" or "EFSS". In this mode, the stepper motor can be accurately started or stopped at any predetermined position, i.e., started or stopped error free.
The second mode is high speed operation, generally designated "slewing". In slewing, the stepper motor is initially operated in the EFSS mode, ramped or accelerated to slew speed, operated at slew speed for a predetermined time and then decelerated to EFSS speed in order to permit accurate positioning.
In a principal aspect, the present invention is an improved circuit for selectively initiating the deceleration of a stepper motor after operation in the slew mode. The deceleration initiation circuit includes a monitor system, an input system, and a comparator system. The input system provides a selectable deceleration signal representing a predetermined time and a corresponding drive pulse (within the series of drive pulses received by the stator of the stepper motor) when deceleration is to begin.
The monitor system is coupled to the stepper motor and monitors or counts drive pulses. The monitor system responsively provides a monitor signal representative of each drive pulse received by the stator.
The comparator system receives and compares the selectable deceleration signal and the monitor signal generated by the input system and monitor system, respectively. Whenever a predetermined relationship exists, the comparator system provides a deceleration initiating signal, and in response thereto, deceleration of the stepper motor commences.
It is thus an object of the present invention to provide an improved circuit for initiating deceleration of a stepper motor. Another object is an improved, simplified deceleration initiating circuit.
Still another object of the present invention is an improved deceleration initiation circuit for a stepper motor wherein the deceleration initiation point is selectable. It is also an object to provide a circuit for selectively controlling the initiation of deceleration in a stepper motor whereby the average time for deceleration over a series of long and short traverses is substantially minimized. Yet another object is a reliable deceleration circuit for a stepper motor capable of providing stable, accurate and repeatable deceleration.
These and other objects, features and advantages of the present invention are described or apparent in the following description of a preferred embodiment.